Glass coloring ions

Color. Many water samples have a yellow to brownish-yeUow color which is caused by natural substances, eg, leaves, bark, humus, and peat material. Turbidity in a sample can make the measurement of color uncertain and is usually removed by centrifiigation prior to analysis. The color is usually measured by comparison of the sample with known concentrations of colored solutions. A platinum—cobalt solution is used as the standard, and the unit of color is that produced by 1 mg/L platinum as chloroplatinate ion. The standard is prepared from potassium chloroplatinate (K PtCl ) and cobalt chloride (C0CI26H2O). The sample may also be compared to suitably caUbrated special glass color disks. 

The colors obtained depend primarily on the oxidation state and coordination number of the coloring ion (3). Table 1 Hsts the solution colors of several ions in glass. AH of these ions are transition metals some rare-earth ions show similar effects. The electronic transitions within the partially filled d andy shells of these ions are of such frequency that they fall in that narrow band of frequencies from 400 to 700 nm, which constitutes the visible spectmm (4). Hence, they are suitable for producing color (qv). 

Cobalt glass, color, 7 331 CobaltCII) hexaaquo ion, 7 229 Cobalt hexahydrate, analysis, 7 237t Cobalt high temperature alloys, 7 223-224 Cobalt hydroxide, analysis, 7 237t Cobalt(II) hydroxide, 7 230 uses, 7 240t... 

Details of the coloration of glasses due to ligand field effects are further complicated by the possibility of redox interactions between two or more different transition metal ions. Other elements such as arsenic and antimony, which do not directly affect color, may alter the oxidation state of a coloring ion and alter the color of the glass. Changes in furnace atmosphere can also inadvertently alter the oxidation state of coloring ions due to changes in the concentrations of O2, CO, CO2, and H2O vapor. 

Cobalt as a Colorant in Ceramics, Glasses, and Paints. Cobalt(II) ion displays a variety of colors in soHd form or solution ranging from pinks and reds to blues or greens. It has been used for hundreds of years to impart color to glasses and ceramics (qv) or as a pigment in paints and inks (see CoLORANTS FOR CERAMICS). The pink or red colors are generally associated with cobalt(II) ion in an octahedral environment and the chromophore is typically Co—O. The tetrahedral cobalt ion, Co—chromophore, is sometimes green, but usually blue in color. 

There are a number of ways to obtain color in a ceramic material (1). First, certain transition-metal ions can be melted into a glass or dispersed in a ceramic body when it is made. Although suitable for bulk ceramics, this method is rarely used in coatings because adequate tinting strength and purity of color caimot be obtained this way. 

Organic acids yield lemon-yellow zones on a blue background [1]. Halide ions migrate as ammonium salts in ammoniacal mobile phases and are also colored yellow. The colors fade rapidly in the air. This can be delayed for some days by covering the chromatogram with a glass plate. 

The purple color of old bottles exposed to the sun for a long time is due to Mn04 ions. These are formed when ultraviolet light oxidizes manganese compounds in the glass. 

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